In the past, circuit-switched networks were used to carry voice traffic from one subscriber to another, while separate packet-switched networks were used to carry data traffic. Two networks were used because the existing protocols and technology available for packet networks did not provide certain characteristics necessary for voice-band calls, such as low latency and deterministic quality of service. Improvements in packet network protocols and technology which address these deficiencies allow a new kind of packet network, sometimes called a “converged network,” to carry both voice and data traffic.
The equipment that interfaces a converged packet network with a circuit-switched network is referred to as a “voice gateway,” a “media gateway”, or a “voice-over-packet gateway.” The voice gateway interfaces with one or more call controllers on its trunk side, and with one or more integrated access devices (IADs) on its subscriber side. The IAD provides a link to the packet network and to the voice gateway for multiple subscribers. The call controller directs the voice gateway to make voice connections. In a circuit-switched network, call control is performed by a telephony switch, for example a Class 5 or a Class 4 switch. In a convergence packet-network, call control is performed by a “softswitch.” Several different call control protocols are in use by different switches.
Migrating from the circuit-switched network to the converged network is an evolutionary process, so that for some period of time many customers will be reachable only through a circuit-switched network. Yet all customers expect the ability to call from one telephone to any other telephone, regardless of what type of network the originating and terminating telephones are located on. Therefore, converged networks will need to interface with circuit-switched networks as well as other converged networks. Thus a need exists for a voice gateway which can support multiple call control protocols and interface with different types of telephony switches and different types of softswitches, simultaneously.